Known such valve arrangements without the control device according to the present disclosure require specific hydraulic elements in specific hydraulic circuitry for realizing several functions, especially safety functions.
For instance realizing a tensioner and compensator isolation, especially in a marine riser tensioner and/or in a drill string compensator, requires a pilot accumulator, charged with a highest pressure at either side of a normally open isolating valve for fluidically isolating a hydraulic cylinder from a pressure accumulator.
Further, a pressure sensing valve for sensing said pressure on a cylinder side and on an accumulator side is required to compare said pressures with each other. Accordingly, a suitable hydraulic circuitry of these hydraulic elements is required, to realize a safety function of closing said isolating valve because of a sudden pressure drop due to a failure, that is, if a wire rope—which is connected to said hydraulic cylinder and carries a load—fails on said cylinder side and/or if a gas leak occurs on said pressure accumulator side. Said highest pressure then causes said pressure sensing valve to shift in a position where said isolating valve will be closed and thus prevent damage from said hydraulic cylinder by interrupting said flow path between said hydraulic cylinder and said pressure accumulator. In case of said wire rope failure the damage would occur due to a sudden release of energy stored in said pressure accumulator which would cause an uncontrolled high speed run away, especially extending, of a piston rod of said hydraulic cylinder. In case of said gas leak the damage would occur due to a loss of a load carrying capability of said hydraulic cylinder and said piston rod would retract uncontrolled at high speed. In both cases a high impact would occur when said piston rod would reach an end of its travel. Additionally, for the purpose of overruling said tensioner and compensator isolation function for special operations, further hydraulic elements would be needed like switching valves for keeping said pressure sensing valve open or closed, respectively.
In order to realize further functions, especially safety functions, with the same valve arrangement, for example a riser anti recoil system, further hydraulic elements would be required, like a proportional flow shut off valve on said cylinder side and a flow shut off valve, especially formed as a switching valve, on said accumulator side. Likewise a further switching valve would be needed for a keep open function of said flow shut off valve.